Hi folks I think this question may have been asked before but I have a Zenoah copy engine which wont rev past 5200rpm it has loads of grunt and will turn a 18x10 prop at 5200 but it also turns a 16x8 at the same revs. I believe the problem is in the transfer port timing but I am unable to work out by how much I need to raise the ports by! Any comments advice greatfully received. The ports are at 24mm from base of barrel to port top also there are 4 ports.
John.

Perhaps it has a built in rev limiter.
If it were the port timing there would be a little variation in the rpm, but not with a rev limiter.

Just a thought.

Everyone speaks and thinks about port timing in degrees. If you will make a degree wheel and post information the answers will probably be better.

Bill

Yeah, port timing is all figured in degrees, but I don't think that's your problem. Possibly a built in rev limiter. Of course this is assuming that the engine is in good shape to begin with. An exhaust port choked with carbon, a dirty stock muffler or air cleaner, etc., etc. etc. could also cause this.

AV8TOR

circlip: what do you mean by copy engine? Thanks Capt,n

Hi by copy I mean it is a SIKK engine it is brand new I have removed the flywheel and mag replacing it with a ZDZ ignition unit and a slightly different walbro carb. The exhaust is a standard unit with the guts ripped out and a larger outlet pipe. I have also tried it with a MVVS tuned pipe and it makes no difference. I dont think that there is an external limiter but I do still think that it is a port timing issue. But I am open to being proved wrong.
Regards John.